ER+
Meaning of ER+: The most common receptor result in breast cancer, and the one that opens the door to hormone-blocking treatment taken over years.
Definition of ER+
ER-positive, written ER+, means that laboratory staining has found estrogen receptors in a sample of cells, most often breast cancer cells. The receptor lets estrogen switch on growth signals inside the cell, so an ER-positive cancer is one whose growth can be driven by the hormone and slowed by treatment that blocks or removes it.
How is the status decided?
A piece of the tumor taken at biopsy or surgery is treated with an antibody that sticks to the estrogen receptor, and a stain makes the bound antibody visible under the microscope. A pathologist then reports the proportion of tumor cell nuclei that have stained and how strongly. Even a small but definite proportion counts as positive, because tumors with low levels can still respond, and results close to the threshold are reported as low positive so the uncertainty stays visible rather than hidden. Laboratories follow standardized methods and run controls, since the result determines years of treatment and a false negative would remove an effective option.
What does a positive result mean for treatment?
| Approach | How it works |
|---|---|
| Blocking the receptor | A drug occupies the receptor so estrogen cannot activate it |
| Lowering estrogen | Aromatase inhibitors cut production in tissue outside the ovaries after menopause |
| Suppressing the ovaries | Injections or surgery stop the main source of estrogen before menopause |
| Degrading the receptor | A drug causes the receptor itself to be broken down |
Which is used depends on menopausal status and on the rest of the tumor profile. Drugs that occupy the receptor belong to the class known as the selective estrogen receptor modulator, so called because they block the receptor in breast tissue while acting on it in others such as bone.
Why does the benefit not last forever?
ER-positive breast cancer generally grows more slowly than receptor-negative disease and responds well at first, but some tumors adapt. The receptor gene can mutate so the receptor stays switched on without estrogen; cells can start using other growth pathways instead; or the receptor can be lost altogether. This is why endocrine treatment continues for years rather than months, and why an ER-positive cancer can return long after the first several years have passed, a late pattern that differs from receptor-negative disease. Receptor status is often retested if the disease returns, because it can differ between the original tumor and a later deposit.
Also known as
Used in a sentence
Hormone-blocking therapy was considered given the tumor's ER-positive status on pathology testing.
Good to know
An ER-positive tumor may still stop responding to hormone-blocking treatment over time, which is why monitoring continues even when receptor status suggests such treatment is likely to help.